HA WAIl AGRICULTURAL EXPERIMENT STATION.

J. G. SMITH, SPECIAL AGENT IN CHARGE

BULLETIN No.6.

MOSQUITOES IN HflWflll.BY

D. L. VAN DINE,

ENTOMOLOGIST, HAWAII AGRICULTURAL EXPERIMENT STATIONe.~

UNDER THE SUPERVISION OF

OFFICE OF EXPERIMENT STATIONS.

U. S. Departrnent of Agricultul~e.

HONOLULU:HAWAIIAN GAZETTE COMPANY, LTD.

1904.

.HAWAII AGRICULTURAL EXPERIMENT STATION,HONOLULU.

[Under the supervision of ~\. C. TRUE, Director of the Office of Experi­n1ent Stations, United States Departn1ent of Agriculture.J

STATION SfAFF.

JARED G. SMITH) Special Agent Zit Charge.D. L. VAN DINE) Entolnologist.EDMUND C. SHOREY) Che1Jt1·st.J. E. I~IGGINS, Horticulturist.Q. Q. BRADFORD) Fann Forel1zan.

LETTER OF TRANSMITTAL.

SIR: I have the honor to transmit and recommend for pub­lication as Bulletin No.6 of this station the accompanying articleon "Mosquitoes in Havvaii," prepared under my direction by lVlr.D. L. 'Tan Dine.

.i\s a result of the efforts of public-spirited citizens a "rnos­quito catnpaign" is now in progress in Honolulu. It has beenfound possible by vvatchful vigilance and proper methods tokeep this tropical city almost free of mosquitoes. The work issupported by voluntary contributions. }-\ salaried Agentis jn charge, cooperating vvith the Board of I-Iealth ann theI)epartment of Public \!Vorks. The first step was to clean thecity alleys and vacant lots, removing and destroying" tins,bottles, soy tubs and other discarded debris capable of retain­ing water. A few hundred tons of this rubbish were dumpedinto the ocean. .LL\fter this, work of a pernlanent characterwas undertaken, such as the drainage of low-lying places orthe filling in of ponds and holes containing stagnant water.I t has been possible to lessen greatly the annual mosquitocrop in Honolulu and promote the comfort and health of theinhabitants of a tropical city of 5°,000 people at a cost notexceeding $.200 per 111onth.

The ainl of 1\1r. Van Dine in this bulletin is to bring~ thescientific facts concerning mosquito extermination before thepeople of this 1"'erritory in a thoroughly practical manner.1'he rules laid dovvn are the results of three years' work andinvestigation. If these rules are followed with due care andvigilance, lIawaii can soon be well-nigh rid of the Svvarlns ofmosquitoes that rob life in the open air and sunshine of thisParadise of the Pacific of all charnl and cotnfort.

Respectfully,

JARED G·. S:NIITJI,

Special .L-1gen,l in Charge.DR. A. C. TRUE.,

Director Office of Experi11zent 5;tations)fl. S. Departnzent of Agriculture) TIl;rashington~ D. t--:.

Recommended for publication.

A. C. TRUE) Director.

Publication authorized.

JAMES VVILSON, Secretary of Agriculture.

CONTENTS.

PAGE

1 he introduction of mosquitoes into Hawaii. . . . . . . . . . . .. 7Distribution and abundance of lVlosquitoes in Hawaii... 7A general account of n1osquitoes 8

The breeding place of lTIosquitoes..... . . . . . . . . . . .. 9The life-history of mosquitoes 9lVIigrations of mosquitoes. . . . . . . . . . . . . . . . . . . . . . . . . .. I I

The food of adult n10squitoes , . . . . . . . . . . . . . . .. 13lVlosquitoes and disease 14common Hawaiian mosquitoes.................... 14

The abundant mosquito, Culex pipiens ISThe Cuban yellow-fever mosquito, Stegomyia fas-

ciata. . .. . 22

rrhe forest mosquito, StegolTIyia scutellaris 23

Natural enemies and diseases of n10squitoes 23

l\,fethods of" controI 25

'

'I'he

"

}--igure I.

2.

3·4·5·6.

7·

8.

9·10.

I I.

12.

ILLU'STRATIONS.

PAGE

Eggs and larvae of Culex ..... ,............ 8Larva and pupa of Culex, full-grown. . . . . . .. 10

Adult lna1e and fen1a1e of Culex 12

l"ypica1 breeding places of n10squitoes. . . . .. ISA breeding pool on the Station grounds.... J6I~he work of filling at the Station. . . . . . . . . .. 17A typical breeding place in the n1akai districts

of I-I0 1101u1u 18Life-cycle of Stego111yia fasciata 21

A "n10squito poster" issued by the Station 27I>rison labor ditching. a district under the di-

rection of the Citizens' l\losquito Con1··n1ittee, I-Iono1u1u 2R

I'he "tin-can wagon" of the C:itizens' 1V1os-quito C0111111ittee, Honolulu 29

Scovv loaded \Nith tin cans and other contain­ers, ready to be towed to sea. Citizens'

lVIosquito C01111nittec, Honolulu 29

MOSQUITOES IN HAWAII.

(Order, Diptera or true flies. Family, Culicidae).

Previous to the year 1826 n10squitoes vvere unknown inflawaii. During that year they were brought to the port ofLahaina, on the Island of Maui, in the ship "\iVellington H

froin San BIas, lVlexico. 'I'he story, as told by the late Rev.\\1111. Richards,u at that time in charge of the lV1ission Stationat Lahaina, is as follows: Mr. Richards was returning toLahaina one evening and met a native who informed hinlthat there vvas a new ~'fly" in the place. l"he native describedthe insect as being a very peculiar "fly" that made its pres­ence knovvn by "a singing in the ear'" Shortly after this,1\:lr. Richards being on the outlook for the new fly, heardthe "singing\" in his ear and recognized the sound as thatof the 1110Squito, which up to that time had never been seenor heard of in the Islands. f-'urthermore, up to the year1826 there was no word in the Hawaiian language for mos­quito. The native terill is "makika," a corruption of the 'wordnlosquito. Lahaina "'iv·as at that time the port for incomingand outgoing ships. It is easy to understand that the shipscon1ing here were few and far between and how general opin­ion could center on the ship "Wellington" as the carrier ofthe pest.

Since the n10sC]uito introduced in 1826 on the ship "'.;Vell­ington" \ivas a so-called "night" 1110Squito, the writer infersthat tbe species cletern1inecl as Culex l)ipiens Linn., so abun­dant and ,viele-spread here, \vas the one introduced at thatt11llC. 'The two species of Stegoillyia or "da~y" lTIosquitoes\vere i:ltroc.lucecl eluring the present generation.

DIS'1'H.IH.L"'Tlc1N AXD AI1UNDA.NCE OF l\10SQlJITOES IN I~IA\VAIL

The 1110squitoes \vere a long tin1e spreading over theIslands. 'r\iva generations ag'o there were ll1any districts en-­tirely free fra111 this pest. rroday such places are exceptional.In the eighties there \vere no nlosquitoes at l\1aka\vao onthe san1e Island as Lahaina. lVIakawao is some fifty 111iles£ro111 Lahaina "as the cro\¥ flies," vvith a n10untain range

aThe 'writer is indebted to Prof. W. D. Alexander of I-Ionolulu forthis account.

8

nearly six thousand feet in elevation intervening. The build­ing of roads, making settlement and communication possible,and the intimate inter-island communication of late years,has so favored the distribution of this pest that only a lE.;"\vplaces at the higher elevations can offer to visitors the in­ducement that the district is free from mosquitoes.

The abundance of rnosquitoes in Hawaii may be acconntedfor by the facts that up to this time there has been no effortto do away with their breeding places, that the nU111ber ofnatural breeding places is unusually large, and that the pestis not checked at any season of the year by clin1atic cODdi­tions, it being possible for them to breed uninterruptedly dur­ing the entire year.

ffi· .:,.,---

----- ---

A GENERAL ACCOUNT OF 1iOSQUITOES.

To Inake this paper of practical value to the people of l-Ta­·waii in fighting this general pest, the accepted facts regard­ing n10squitoes are briefly given. Dr. L. O. Howard, Ento­·mologist of the United States Departn1ent of .lAgriculture,firstadvanced the idea of the '\vholesale" destruction of this ~n­

sect. His book, "rvlosquitoes,"a is the authoritative work onthe subject. In 1892 Dr. Howard conducted during the SU111-

a Mosquitoes: Ho\v they live; How they carry disease; Ho\v theyare classified; Ho\v they may be destroyed. Howard. 1900.

9

Iuer experim,ents in the Catskill lVIountains, N ew y~ork, thesuccess of vvhich becanle widely known throug'hout thelJnited States. Since that time it has been repeatedly :.lelu­onstrated in different mosquito-ridden sections of the ':oun­try that it is unnecessary for any community to submit tothe rnosquito nuisance. Particularly convincing are the ex­perin1ents being carried on in the State of New Jersey inwhich Dr. J. B. Smith of the New Jersey Experiluent Sta­ti()rl is taking an active interest. The 'work of destruction -isdirected against the breeding places.

rr~HE BREEDING PLACE OF l\!{OSQUITOES.-The post-en1bryonicdevelopment ,of the 'n10squito~ that is, the interval betweenthe egg state and the adult winged form, occurs entirely be­neath the surface of water. The young during this portionof their life-cycle are true aquatic insects with one excep­tion, they do not breathe the air dissolved in the water as dofish, but by a special structure, a respiratory siphon (see fig­ure 8 C), breathe the free air above the surface of the vva­ter; deprived of this ihey perish. By nature of their structurethe young of mosquitoes can develop only in water and thenonly under certain conditions. As a rule mosquitoes breed insmall collections of standing fresh vvater. Specimens aresometimes found in streams and some species are kno'vvn tobreed in salt or brackish water. For all economic purposesthe statetpent is correct that mosquitoes breed only in water,usually stagnant fresh water in artificial places. Do away 'U}iththese places and it beC011zes i111possible for tnosquitoes to breed.

LIFE HISTORY OF MOSQUITOES.-The detern1ination of methodsfor destroying aln inj urious insect inlplies a careful study ofits life-history in order to find the vulnerable point in thelife-cycle of the pest. All insects undergo during their de­velopnlental period relnarkable changes in form, structure andhabits. One can certainly detect no resenlblance betweenthe wriggling larva of the mosquito in the water and theadult winged insect in the air. In the higher animals thereare no distinct periods or stages of developnlent. The youngon hatching from the egg or at birth resemble the parent withthe exception that they are smaller in size and undeveloped,but as growth continues they gradually acquire the size andcharacteristics of the adult. The life history of insects, onthe other hand, is, generally speaking, divided into three dis­tinct stages after hatching from the egg: the young or lar­va, the gro\ving stage in the life of the insect; the pupa, aperiod of development during which a wonderful change ortransformation in the form, structure and habits occurs; and

10

the adult or winged insect, the form we usually recognize.The eggs of the common mosquito, Culex, are deposited on

the surface of standing water. (See figure I.) Under theright conditions of temperature they hatch in about twenty­four hours. The larvae develop to their full size in thecourse of eight to'fourteen days during which time they moultor cast off their outer covering several times to prov-ide for

Fig. 2.-Full-gro\vn larva at left and pupa at right of Culex, enlarged,showing "swimming- flaps" of pupa at right, below, greatly enlarged.(From Howard, Bul. 2::;, new series, Division of Entomology, U. S.Department of Agriculture.)

increase in size. (See figure 2.) The developn1ent of thelarvae depends on the ten1perature of the water and thefood supply. Their food consists of the plant and animaln1atter, often luicroscopical in size, COln111011 to standingwater.

'The pupa of the n10squito is also aquatic, norn1ally restinginactive at the surface. (See figure 2.) This is the periodduring which the 1110Squito transforms fro111 an aquatic in­sect to one of the air. 1~he young or grovving stage has

II

passed. The pupa takes no food and moves only ,vhen dis­turbed as a Inatter of protection. The pupal stage is muchshorter than the larval. In two or three days the pupa trans­forms to the adult mosquito and becomes the notorious house­hold pest, the entire life-cycle being a matter of eleven toeighteen days.

rfhe only remedy for adult mosquitoes is protection byscreening, or the burning of insect powder. These remediesbring only temporary relief and do not ren10ve the source ofthe nuisance. The in1portance, then, of not allowing mos­quitoes to develop beyond the pupal or final aquatic stage isevident. No practica:l nzethod of destroying adult 111osquitoes isknown,.

rfhe length of the life of adult mosquitoes varies. It is dii-~

ficult to get insects to repeat correctly in confinen1cnt ""hattheir life-history and habits \vould be under natural condi-­tions; therefore the length of the life of the adult cannot be·detern1ined by experirnent. As a rule the n1ale5 of insects..do not live any g'lreat length of tilne after tnaturity, and the­fernales die soon after depositing their eggs. I!l a tropicalcountry, like Hawaii, where no difficulty is encountered bythe gravid female in securing favorable breeding places.;throughout the year, the length of the adult life is probably-­at the most only a matter of several weeks. In cold conn-·tries the male mosquito\es are known to die in the early '.iVin-·ter and the females hibernate during the cold season, a perio·d:of several n10nths, until suitable conditions for egg-laying­pre·vail.

l\1IGRATIONS OF MOSQUITOES.-The adult mosquito (see figure3) is a very feeble flyer and is usually found in the vicin­ity of its breeding place. Instances are on record \vheremosquitoes have been carried in large numbers for long dis­tances by the wind, but invasions from one locality to an­other are exceptional. It is well.known that on windy daysn10squitoes are less in evidence and the general belief is that:they "have been blown out to sea." It is evident from thestructure of their organs of flight that mosquitoes cannot longendure in a high wind. In an infested locality, mosquitoes arealways in evidence in1mediately after a wind subsides, es­pecially in places where the vegetation is abundant, in thefoliage of which they seek shelter from the wind. Smithsays that the habits of mosquitoes in regard to their flyingany distance varies with the different species. He discussesa

aSpecial Bulletin T. New Jersey Experiment Station.

12

:a salt-water species, Cule."r sollicitans, which is appar"ently atrue migratory form. It can be stated without qualificatio1ls.that the source of mosquitoes is generally the iln1Jlediate vicinity,of the infested pla:ces.

The above statement is subject to exceptions as provedby the observations of Mr. H. W. Henshaw, the well-kno"vnnaturalist of Hilo, Hawaii. T'he writer has not observed evi­dences of migration among the species of mosquitoes occur­ing in these Islands. Invariably the source of tTIosquitoes in­festing any district has been found to be nearby natural and

~

~

Fig. 3.-Adult fen1ale above and male below of Culex. (From Ho\vard,Bu!. 25, new series, Division of Entomology, U. S. Department ofAgriculture. )

:artificial collections of "vater, usually artificial collections inthe immediate vicinity. IVlr. Henshaw in speaking of inva­:sions of mosquitoes says in a letter to the writer:

So far as my own observations extend such accidental- invasions ofmosquitoes are rare in these Islands, the insects here as a rule being ex­tremely local. Nevertheless that such accidental dispersal of the pests

13

in the Islands does actually occur is proved by an instance in pointwhich came under mv personal observation in June, 1899, at Pahala,Kau (Island of Hawaii). Mr. C. M. Walton, the then manager of theplantation, informed me that prior to the visitation of the pests aboutto be described, mosquitoes were practically unknown about the village;if found at all it was in such small numbers as to cause no annoyance, andmosquito-nets were unknown.

In the spring of 1899 there was an unusual quantity of waste waterfron1 the mill and this ran down to the flats about a mile below andthere formed a series of small ponds aggregating a considerable expanseof shallow water. l~ot long after the formation of the ponds swarms ofmosquitoes made their appearance about the mill and in all the dwellings,evidently brought there by the strong trade winds which blew directlyfrom the ponds. At the time of my visit the mosquitoes (Culex pipiens)put in an appearance about dusk and soon rendered life a burden andsleep impossible except under nets which every householder had beencompelled to provide for every bed.

A few days later I visited the Kapapala Ranch, distant from Pahalaabo'ut four miles in an air line and about five miles from the ponds inquestion and there found a similar state of affairs. Mr. Julian Monserratt,manager of the ranch, told me that the invasion occurred at the sametime as at Pahala prior to which no mosquitoes had been seen at or nearthe ranch headquarters where, indeed, there was no possible breedingplace for them.

Unquestionably the clouds of mosquitoes originated in the sameponds below Pahala and were carried by the trade winds not only toKapapala but for miles over the surrounding country in the direct trackof the breezes. At Pahala, at least, the colonization has proved to bepermanent as here, as elsewhere on cane plantations where water flumesare in use, leaky flumes form smaIl pools at many points along theirtrack \vhich make ideal breeding places for mosquitoes.

At the tilne I speak of, comparatively little information had reachedthe general public in relation to the methods of abating the mosquitonuisance, though Mr. Walton had tried experiments \vith kerosene onSOlne of the pools, if I remen1ber correctly, with poor success and theyhad been abandoned. With our present knowledge of the use of theheavy crude petroleun1s it cannot be doubted that prompt and regulartreatment of the ponds in question with proper oil, together with fre­quent inspection and treatlnent about the village itself, would have abatedthe nuisance within a reasonable time. In eternal vigilance and in promptrelnedial measures alone lies safety from mosquitoes in the tropics.

lVIr. l-Ienshaw has since inforlned the vvriter that the pondsInentioned are quite exposed and unsheltered by vegetation,and agrees with the writer that had the ponds been surroundedby trees or had vegetation intervened to vvhich the insectscould have clung for shelter, the distribution would not, prob­ably, have been so widespread.

TIlE FOOD OF ADULT MOSQUITOEs.-Their food consists of theblood of animals and the juices of plants and fruits. Mos­quitoes are normally plant-feeding insects and only the femaleis a blood-feeding insect when that is obtainable. 'The malesatisfies his appetite on the juices of fruits or other liquidssince the proboscis is not constructed, as is that of the fe­male, for piercing anything vvith any degree of resistance, als

the skin of animals or the epidermis of plants. Ho\vard says,speaking· of fen1ale mosquitoes: "It is safe to say that only

"

14

an infinitesimal proportion of them ever taste the blood of awarm-blooded animal."

MOSQUITOES AND DISEASE.-The greatest impetus to the war­fare against mosquitoes was given by the recent positive demon­strations that certain species are the carriers of disease, that is,the agents (germs) responsible for the disease are parasitic tocertain mosquitoes during an intermediate stage in their develop­mental cycle. In fact it has been proved in the case of yellow­fever and malaria that \vithout certain species of mosquitoes ashosts, the life-cycle of the organisms responsible for the diseaseis interrupted. This has changed the mosquito problem fromone of discomfort alone to one of health also. The most com­plete work in preventive m,edicine is the result of experim~nts

along these lines. That yellow-fever and malaria are conveyedfrom diseased persons to healthy people by the bites of certainspecies of mosquitoes is an acknowledged fact in recent medicalliterature.

Aside from yellow-fever and malaria, mosquitoes are credited. with the· dissemination of elephantiasis, filariasis, and possibly the

dengue fever and leprosy. The relation of certain insects to dis­eases, both plant and animal, is a study \vhich in the future "Vvill domuch to prevent their present serious \vork.

THE COMMON HAWAIIAN MOSQUITOES. R

The abundant mosquito in Hawaii, known locally as the"night" mosquito, is a species of the well-known genus Culex,Culex pipiens Linn. All members of this genus taken generallyfrom the Islands of Hawaii, Maui, Oahu and Kauai belong tothis one species. The vicious "day" mosquito proved to be thedangerous Cuban yellow-fever mosquito, StegoJnyia fasciataFabr.b Another species of this genus, Stegu111yia scutellarisWalker, occurs here but is not so abundant in the towns and citiesas the former species and, being found to a great extent breed­ing in small natural collections of water in the forest, such asthe leaves of plants and the hollow decayed stumps of trees andbranches, it is referred to as the forest mosquito to distinguishit locally from the yellow-fever species.

aThe specimens from which the determinations were made wereforwarded to Dr. L. O. Howard, Entomologist of the United States De­partment of Agriculture, and were examined and reported upon by Mr.D. W. Coquillett of the Division of Entomology.

bThis species is recorded from these Islands by Grimshaw underthe name Culex taeniatus Wied. Fauna Hawaiiensis. Diptera. Vol. III,Part I, p. 6.

THF ABUNDANT MOSQUITO,- Culex pipiens~-The members of :the genus Culex are distributed generally -over the world and seem to be limited by neither altitude nor climate. The species so abundant here, Culex pipiensJ is the common species of the genus and the mosquito whose life-history and habits are most generally known. This mosquito is reported from all parts of the United States and is recorded by Theobald as occurring gen­erally in Europe.

BREEDING PLACES.-The places chosen by the female of this

Fig. 4.-Typical breeding places of mosquitoes.

species for depositing her eggs are many and varied. (See figure 4.) There is, however, a decided preference for certain places. Where there is a choice between water containing a supply of decomposing vegetable or animal matter and u~contaminated

water, the insect will invariably choose the water containing the organic matter, serving as it does as food for the young.

16

The above fact was nicely shown in observations at the Sta­tion last year. Several attempts had been made the previous year to dig a cess-pool. The nearness of the rock to the surface of the ground necessitated abandoning several sites. Two of these were deep .enough to retain the surface water which drained into them. The yard-boy used one of these depressions (see figure 5) to throw the sw.eepings of the yard-grass, leaves, weeds, etc. When the writer made a survey of the Station grounds to locate the breeding places of mosquitoes these t,vo

Fig. S.-A breeding pool found at the Station, almost completely hidden by the dense foliage about it.

places were found within two hundred feet of the laboratory. A person could, however, walk within a few feet of either place and not observe the presence of water, so dense was the growth of vegetation about them. The larger one, containing the decay­ing refuse, was about six feet across and its greatest depth was a little over one foot. The water of this pool was literally a living mass of wrigglers or the young of mosquitoes. A small ladle, used for collecting larvae, ,vas dipped into the center of the pool and over two hundred larvae by actual count were obtained by the one operation. The capacity of the ladle ,vas three ounces. On- the following morning,]anuary 16, 1903, the writer collected one hundred and eighty-five egg-clusters from the sur­

17

face of this pool. An egg-cluster is the product of one female and contains from two hundred to three hundred eggs.

The other excavation, somewhat smaller in diameter, did not at first appear to contain wrigglers but closer observation showed that larvae were present· though not in numbers comparable to the first pool. When regarding the place as a possible source of mosquitoes, however, the conditions were sufficient for it alone to play an important part in the general discomfort of« the sur­rounding community. This second pool was found, by aid of the dip-net and ladle, to contain, at least, several thousand larvae. Here and there about the margin the egg-clusters were found the following morning.

Fig. 6.-Filling in breeding places at the Station.

The conditions regarding the temperature, location and source of the water were exactly the same and the writer can account for the great difference in the numbers of the larvae in the two in­stances in no other way than that the gravid female chose the pool containing the decaying vegetable matter in preference to the one containing the clear water. These places were promptly filled in (see figure 6) and removed for once and all time as pos­sible breeding places for mosquitoes.

The places mentioned by different writers as the breeding places of this species of mosquito are \vater-tanks, tubs and buckets un­der water-taps, wells, cisterns, barrels,. open sewers, cess-pools,

I8

,swamps, small pools, wayside ·ditches, empty oil ti.ns~ biscuit tins, sardine and tomato cans, :gourds,.flower pots,vases, cuspidors, broken and ,unbroken bottles, crockery, pott'ery and tins on rub­.bi~h heaps, hollow stumps, post-holes and- other excavations left unfilled, fire-buckets, gutters and eaves which are imperfect or ,which have become clogged, water-traps in sinks and clos.ets, ,watering-troughs for stock, neglected lily ponds and fountains, -and catch basins from leaders.

Aside from these typical places the writer ,has taken the .larvae from tins containing water, placed under the legs of -tables and m,eat-safes as a protection against ants, a common practice here, from urns and flower vases on graves in ceme­teries, from beneath racks used in washing wagons, from water-

Fig. 7.-A typical breeding place in the makai districts of Honolulu.

butts and sunken reservoirs in blacksmith shops and carriage fac­tories used in cooling horse-shoes and \vagon-tires, and from the ,hoof prints of a cow near the edge of a rice field. As to the amount of water necessary for breeding purposes, the vvriter has found this mosquito breeding in a small beaker containing less than three ounces of water. A person might reason that if a ·small container would breed mosquitoes, a larger one would be .even a greater source. This is no doubt true when comparing a small beaker containing a few ounces with, for example, a tub ·of water, but as far as the experience of the writer goes, a --tub -of standing water may be as prolific a breeding place as a pond ,or- pool containing many hundred times the volume of water.

19

Close inspection alnd treatment of the typical breeding places)

111ai11'zy artificial) as enu7nerated above) will rid G'l'l'jl infested local­ity of this 1nosquito.

,The frequent rains which only occasionally are abundantenough to form streams, do form, however, natural breedingplaces in the uneven beds of streams and ditches and surface ofthe ground. This is especially true in the makai districts havinga costal plain of any width. (See figure 7.) In the mauka re­gions these collections of water are not permanent owing to theprevailing steep slope and the general looseness of the soil af­fording natural drainage. These small collections of vvater on thelower levels, of long duration during the rainy season, createnumerous breeding places for this species which continue untilthe ,vater disappears under the action of the wind and sun in thedrier seasons. Communities situated in such localities in theIslands have a more serious problem before them in any effortto reduce the numbers of mosquitoes. FillinK in or drainingor the regular use of oil during G season of rain are the only reme­dies for these places.

LIFE-HISTORY OF Cule.'!C pipiens.-( See figures I, 2 and 3.)The eggs of the "night" mosquito are easily observed in theplaces where they occur. They appear a raft-like mass floatingon the surface of the water and resemble a small piece of charcoalabout one-fourth of an inch in length. This manner of deposit­ing the eggs is characteristic of the members of the genus Culex.The egg-mass or "raft" is the product of one female and accord­ing to Theobald is "laid soon after sunrise and also at dusk if theweather is warm and stil1."a Examination under a hand-lensshows a distinct structure to the mass, it being made up of indi­vidual eggs, standing close together in an upright position, thebottom of the egg being larger than the top, thus making theraft boat-shaped. Each raft is estimated to contain from twoto three hundred eggs, the individual egg being hardly visible toone unaccustomed to looking at objects so small. The lightnessof the mass insures its floating on the surface. Howard saysthat if the eggs are kept completely immersed the larvae willnever develop, this being because of the inability of the develop­ing embryos to obtain the necessary air supply. The peculiarstructure of the bottom of the eggs prevents the water fromactually wetting them.

When the eggs hatch they open downward letting the larvaeinto the water. This occurs from twenty-four hours, under favor-

aA Monograph of the Culicidae of the World. Theobald. 1901.

20

able conditions, to two or three days, after the eggs are deposited..Naturally the young on hatching are very small but develop in afew days into fair sized wrigglers. These are the common na­tural history objects of the rain-water barrel which, as youngsters,.we all believed were "rained down."

The larva of this species is found normally at the surface ofthe water with its head in a downward position. The expla..nation of this peculiar position is this: the larvae of this andall species of mosquitoes, though aquatic as regards living in andobtaining their food from the water, are true air-breathers andmust necessarily come to the surface to obtain the air. Hovv thi~

operation is performed is shown in the figure of the larva. The­larva while breathing at the surface continues to feed beneath;,hence the position of the head downward. It moves awaywhen disturbed and can frequently be seen foraging about in thewater for food but coming regularly to the' surface to breathe.Its food consists of the decaying organic nlatter and the micro-­scopical organisms common to standing water. Only one conl-'ment in favor of the generally condemned mosquito can be foundand that is in regard to the larvae. Comstock says: "The larvaeof mosquitoes are doubtless beneficial insects, for they feed on thedecaying nlatter in water, and thus act as scavengers," and thenhe adds, "but the annoyance caused by the bites of theadult female more than balances this good." The length of thelarval life was found to vary under different conditions from sevento fifteen days.

At the last larval moult, the pupal stage begins. The pupa isan ungainly looking creature resting quietly at the surface, tail­end down\\Tards and further distinguished from the larva by itsbig head. This "head" is really the head and thorax of the insectfused together. The pupa has also tvvo breathing-tubes, insteadof one, rising, not from the tail-end of the body but fronl theupper side from that portion knovvn as the thorax. The end ofthe abdomen is supplied with tvvo broad flaps (see figure2) used for swimming, with which by vigorous nlotionsof the body the insect drives itself down into the water when dis...turbed. The nlanner in which the pupa rises to the surface \vith­out effort demonstrates that its weight is less than that of thewater. The characteristics of the structure of the pupa are wellillustrated in the figure. The length of the pupal stage is a mat­ter of about two days.

rrhe length of the life-cycle of Culex pipiens vvas obtained byplacing eggs laid the previous night (collected in vessels exposedfor the purpose) on water of ordinary temperature. The water

·

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was kept shaded and no food was added. The eggs were placed -in the breeding jars on January 16. They hatched in the fore­noon of January 17. The first larvae changed to pupae ,on Janu­:ary 3 I. The first adults issued from the pupal cases on February 2. The life-cycle in this instC;lnce was 17 days.

Fig. 8.-Life-cycle of Stegomyia fasciata. (From Bul. No. 13, Yellow Fever Institute, U. S. Public Health and Marine Hospital Service.) A. Upper and side view of a single egg, greatly enlarged B. Full­grown larva, enlarged. C. Breathing-tube or respiratory siphon of larva, greatly enlarged. D. Pupa, full-grown, enlarged. E. Adult female. F. Adult male.

To illustrate the effect of temperature on the hatching of the eggs, several newly laid clusters were placed on ice-water and put in an ice-chest. These did not hatch until three days after­ward, \\Thile on the other hand egg-clusters collected the same day, December 23, 1902, hatched the same afternoon.

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THE YELLOW FEVER MOSQUITO) Stegon~yia fasciata.- ( Seefigure 8.) This mosquito is the notorious yellow-fever species ofCuba. Just how or when it came to these Islands is unknown.Dr. Howard under date of January 27, 1903, writes: "The twospecies of Stegomyia listed (from HC;lwaii) occur throughout theEast Indies." P'rof. V. L. Kellogg of Stanford University, inwriting of his trip to the SalTIOan Islands a year ago says: "I aminterested to learn that your day mosquito is the yellow-feverchap, Stegomyia fasciata. That is just whatI found the Samoanmosquito to be. * * * This is the abundant Samoan mosquitoand the one which presumably disseminates elephantiasis."

The dissemination of yellow-fever by the mosquito is not anew idea. Dr. Carlos Finlay of Havana, Cuba, was of the opinion, •as early as 1881, that this disease was conveyed by this pest.This theory was proved a fact by a commission of surgeons of theUnited States Army by demonstrations made in Cuba in 1901.They proved beyond all doubt that this species, Stegonlyiafasciata) was a conveyor and perhaps the only conveyor of thisdreaded disease. There is no record of there ever having been acase of yellow-fever in these Islands. Certainly the quarantineregulations have not up to this time been responsible for the im­munity from this disease, for it was not known until IgOI whatthe proper quarantine against yellow-fever was. The reason forour immunity is made clear in a statement by Dr. Geo. M. Stern­berg, Surgeon General (retired) of the United States Army.In an articlea on the transmission of yellow-fever by mosquitoes,he says:

The propagation of the disease depends upon the introduction of aninfected individual to a locality 'where this mosquito is found, at a sea­son of the year when it is active. Owing to the short period of incuba­tion (five days or less), the brief duration of the disease, and especiallyof the period during which the infectious agent (germ) is found in theblood (three days), it is evident that ships sailing from infected ports,upon which cases of yellow-fever develop, are not likely to introduce thedisease to distant sea-ports. The continuance of an epidemic on ship­board as on land, must depend upon the presence of infected mosquitoesand of non-immune individuals. Under these conditions we can readilyunderstand why the disease should not be carried from the West Indiesor from South America to the Mediterranean, to the east coast of Africa,or to Asiatic seaport cities. On the other hand, if the disease could betransmitted by infected clothing, bedding, etc., there seems no good rea­son why it should not have been carried to these distant localities long ago.

The safety this country has enjoyed in the past, due, it is seen,to the length of time it has taken a vessel to come here fromyellow-fever infected ports, is removed by the intimate relationsabout to be established by a new line of steamers between hereand the Mexican coast. The possibility of the completion of the

aSmithsonian Report. 1900. p. 670.

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Panama canal in the near future gives additional cause for pre­caution against the introduction of the most dreaded of tropicaldiseases. •

The yellow-fever mosquito is well named a "town" species.It breeds almost exclusively about dwellings, and authorities statethat it is seldom found far outside city limits unless in the vicinityof dwellings. The female will invariably choose small collectionsof clear water for depositing her eggs. The eggs are laid singlyon or near the water and if not on the water may remain dormantfor a long time until washed into the water or, as in the case of arain-barrel, until a shower brings the water to their level. At­tention to the artificial collections of waler about dWlellings willbe the principal factor in reducing the 11/U1nbers of this spec£es.

THE FOREST MOSQUITO) Stego11~yia. scutellaris.-This speciesand the yellow-fever mosquito are known locally as the "day"mosquitoes. While Stegotnyia scutellaris breeds in such places asmentioned in connection with the yellow-fever species, it differsfrom the latter in that it is not restricted to such collections ofwater. The writer has often found it breeding in small bodiesof water in the forest. These places have been sometimes far re­moved from habitations and on several occasions have been dis­covered where, the writer ventures to say, not more than oneperson would visit, on an average, in a year's tin1e. These na­tural breeding places are such small amounts of water as maybe contained in a hollow stump of a tree or limb, a depression in astone in the bed of a mountain stream, or the leaves of plants.

On February 25 last, the writer collected what he supposedwere the eggs of the yellow-fever mosquito. These were placedin a breeding jar and hatched on March I. On March 9 the firstpupae appeared and by March I I all had transformed to the pupalstage. The first adult issued on March 12 and proved to bescutellaris. Specimens continued to leave the water until March17, when the last one completed its life-cycle. The life-cycle "maybe summed up as follows: the egg state is five days, the larvalfrom eight to ten days and the pupal three to six. Mating inthis species occurs at any time during the day. The adult infestsfor the most part shady place~.

NATURAL ENEMIES AND DISEASES OF MOSQUITOES.

The dragon-flies or "mosquito-hawks" are the most effectualenemies of the mosquitoes that we have here. The dragon-flies,Odonata, are for the most part members of the single genusAgrion. The number of aquatic species of insects is far less inHawaii than in other countries. In thesearching swampy places

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about Honolulu for the larvae of the mosquito it' was not unusualto dip up with the same dipperful of water from, the net, thelarvae of mosquitoes and the nymplis or young of dragon-flies,while the adult dragon-flies could be seen flying in myriads overthese places. This is significant when it is known that the dragon­fly is predaceous in both the young and the adult forms; theyoung dragon-fly, an aquatic insect, feeding on the larvae of themosquito in the water and the adult preying on the winged insectin the air. This highly beneficial, strong flying and beautiful in­sect is met at all elevations. The writer has seen it on thetop of Mt. Tantalus as well as the other elevations between thatpoint and the beach at Waikiki.

Among our fish we have two efficient enemies of mosquitoes inthe ponds, rice-fields, taro-patches and ditches. They are thegobies, locally known as "oopu" and the gold-fish. In answer toa letter from the writer in regard to introducing into these Islandsthe top-minnow, DT. David Starr Jordan says under date of Janu­ary 21,19°3:

The only fishes that you have that feed upon mosquitoes in thesmall ponds, are the different species of gobies locally known as oopu) andthe gold-fish. The different species of oopu are found in all the streams,but whether they feed on the larvae or not must be determined by dis­section.

I'he top-minnows are entirely unrepresented in Hawaii. They arevery easily transported, being extremely hardy. There are, however, noneof them in California, and they would have to be brought either fromthe Mississippi Valley, or from Mexico. The best species for your pur­pose could be found in the streams of Central Mexico, but it would be alittle costly to send a man down to get them. N ext to these, I wouldrecommend trying the Gulf States or Flonda.

These fish belong to the family of Poeciliidae) and there are manyspecies, nearly all American. The single Japanese species is common inrice ditches in the extreme South of Japan and probably feeds on larvae.

After careful observations, the \vriter is convinced thatamong the fishes, hardly a more efficient enetny could be foundthan gold-fish. A single gold-fish in an aquarium ate overone. hundred and fifty larvae in twenty-four hours' time. Otherspecimens placed in pools containing n10squito larvae wereafter\vards dissected and the stolnach contents were foundto consist ahnost entirely of the remains of the bodies oflarvae. From these experiments, gold-fish were placed inwatering-trough,s, tanks and pools, \vith the result that theyoung of mosquitoes did not develop in these. places. Searchwas made for larvae in lily-ponds and fountains where gold­-.fish occllrr,e,dan;d conditions verified the above experin1ents.

The introduction of insectivorous bats to feed upon adultmosquitoes was suggested. The matter \vas referred to l\fr.Wm. A. Bryan, Curator of Ornithology of Bishop Museum andInspector of Birds and Animals for Hawaii. Mr. Bryan re­plied:

Vesperugo) the commonest of the British bats is found about oldbuildings, in creeks, rocks, etc. Its food is said to be gnats (mosquitoes).It \viII readily eat nleat in captivity and becomes a nuisance in houses. Iwould not advise the promiscuous introduction and liberation of anyspecies.

Concerning natural enemies in his book on "l\10squitoes,"Dr. Howard has the following in regard to Hawaii:

1\:1r. Albert Koebele informs me that he imported into Hawaii fromCalifornia a large number of the \vestern salanlander \vhich \vere liber­ated in the upper part of the Makiki streanl in the hope of reducing thelarge numbers of mosquitoes breeding everywhere in s111all pools and taro­patchs.

IVlr. R. H. Pettit of the Michigan Station lTIentions a a fun­gus, Ento11tOphthora, as destructive to adult lTIosquitoes aboutpools in timber lands. Theobald Inentions another fungusdisease, E1npusa culicis, which also "destroys Culex both inEurope and America."

Efforts have been lTIade to determine son1e artificial methodof arraying natural enemies against the n10squitoes but, withthe exception of the fish, little has been accomplished. In thisconnection, Dr. Howard inforn1s the writer that ('in the mat­ter of control not much can be done with natural enemies.F"'ungus disease has never amounted to anything."

N[ETI-IODS OF CONTROL.

A tropical country is an out-of-door country and the mos­quito problem bCOlTIeS at once a serious question. Heretoforethe only effort directed against the lTIosquito nuisance in theseIslands has been to secure protection from the adult by screen­ing the houses, the use of nets over beds at night and theburning of buhach or insect-powder. rrhese methods are moreor less successful in obtaining individual relief but in no man­ner do they lessen the numbers of the pest or ren10ve thesource of the nuisance. A conservative estimate, based onfigures furnished the writer by the wholesale importinghouses of Honolulu, places the sum annually spent in these

aSpecial Bulletin 17. 1\1ichigan Experi111ent Station.

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°Islands for insect powder, wire mosquito-cloth and mosquito­netting at $27,243.00, of which $7,008.00 is for insect-powder,$9,73.5.00 for wire mosquito-cloth, and $10,5°0.00 for mos­quito-netting. °I'hese figures are based on the retail priceand do not include a great quantity of cheaper grades of openInesh cloth sold to orientals and the poorer classes. A land­lord cannot think of offering a house or room for rent andexpect a ready tenant unless he is able to insert '~mosquito­

proof" in the announcement, and nets are a household neces­sity in homes that cannot afford screening. If the aboveamount of money was judiciously spent in ridding the com­munities of this 'Territory of the breeding places of nlosqui­toes, permanent relief could be secured. In reviewing thelife-history of the 1110Squito it is evident that the fight againstthe adult is futile and that the effort of control must bedirected against the breeding places of the insect.

It is the common opinion here that the taro-patches andrice-fields are mainly responsible for the abundance of thenl0squitoes. These collections of water are not the sourceof mosquitoes. They do breed to sonle extent in these placesbut the writer has found the source of mosquitoes, even inthe ilnmediate vicinity of taro-patches and rice-fields to bell1ainly the nlany exposed receptacles filled with standing\vater, comnlon about the laborers' quarters. It is not in thefields, 111oreover, but about thenl in the clogged ditches andabout the sides, vvhere the \vater re111ains cOlTIparatively shal·­low and unchanged, that the larvae are found. T'he writerhas, hovvever, found that in abandoned rice-fields, where the\vater stands in n10re or less confined areas for a great lengthof time, the larvae do occur in large nunlbers.

In the outlying districts, where city \vater is not suppliedand rain-\vater 111USt be stored for use, the lila11Y containersused for this purpose, especially about the native houses andChinese shacks, are by far the greatest source of n1osquitoes.1~he vvriter has counted as ll1any as seventeen tubs, barrelsa.lld other containers about one nati'v'e house all breeding 1110S­

quitoes in inJll1enSe n UITi bers.Generally speaking, the exterl11ination of the 1110Squito can­

not be acconlplishec1. '"fhe ren1ecly is by a systelnatic and con­tinuous effort to do a\vay with their breeding places or, if thatis not practical, by the proper treatll1ent, to render the con­ditions unfit for tIle developnlent of the larvae. In favoredlocalities this vvill result practically in externlination.

'I'he rules for ridding any particular comrl1unity of nlOS­quitoes are si111ple and effective and do not require any great

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expenditure of money. (See figure 9.). I-'hey may be sum­lned up as follows:

(I) Mosquitoes to breed require water, the larvae being as truly aquatic as fish. To do away, then, with all bodies of

Fig. 9.-The above cut illustrates a "poster" which was printed in five languages (English, Hawaiian, Portuguese, Japanese and Chinese), giving brief rules for exterminating the mosquito, and distributed by this Station throughout the Territory.

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standing water by filling or draining is the first step. (See figure 10.)

(2) Collections of water which cannot of necessity be re­moved, such as water tanks and barrels ~used tor storing "va­ter should be tightly screened to prevent the gravid female from reaching~ them, drawing off the water for use from below.

Fig. IO.-Prison labor ditching a district under the direction of the Citi­zens' Mosquito Committee, Honolulu.

(3) Mosquitoes can breed in water only under certain condi­tions, the main one being a free supply of air above the sur­face, which they obtain by means of breathing-tubes. Bodies of water which cannot be done away with by drainage or protected from adult mosquitoes by screening, should be treated in such a manner as to prevent the developing larvae from obtaining the necessary supply of air. The coal-oil treat­ment, \videly understood, consists in covering the surface of exposed water with a thin layer or film of oil. The oil does not affect the water for use if the water is dra\vn off from below. One ounce of oil will cover about fifteen square feet of surface.

(4) If the us.e of oil is undesirable, for exanlple, in the case of a lily-pond or a watering-trough for stock, thl2 jn­troduction of gold-fish will keep the water free from larvae.

(5) All such artificial containers of water about the door­yard as tin cans, bottles, broken pottery and crockery on

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Fig. I I.-The "tin-can wagon" of the Citizens' Mosquito Committee, Hono­lulu.

rub~ish heaps, etc., should be collected and carted away. (See figure I I.)

(6) Other containers, as tubs and buckets under water­taps, cuspidors, fire-buckets, water in chicken c09Ps and dog kennels, etc., should be frequently enlptied.

Fig. 12.-SCOW loaded with' tin cans and other containers ready to be towed to sea. Work carried on under the direction of the Citizens' Mosquito Committee, Honolulu.

3°

(7) The plumbing about the place shoulclbe carefully in­spected since mosquitoes are known to breed in cess-pools,water-traps in sinks and closets, catch-basins from leadersand in eaves that are imperfect or have become clogged.lVTake the covers of the cess-pools absolutely tight and placea screen over the opening of the vent pipe for egigsdepositedin the closet tank are flushed down into the cess-pool and \villhatch and develop.

(8) The work in any cOllln1unity must be genelal since aneglected tub in one yard can breed enough lllosquitoes tomake an entire comn1unity uncomfortable. It is seen fron1 thisthat though the mosquitoes infesting any household are usu­ally bred in the sanle dooryard and that invasions fron1 anydistance are exceptional, yet to do away with the pest themembers of any con1munity lllust co-operate in the work.

(9) The adult lTIosquitoes seek shelter in weeds, grass,bushes and trees in the vicinity of water. Therefore all suchvegetation about ditches, pools and other collections of \vatershould be cleared a\vay.

It should not be necessary to present in detail t.he argu­ments \vhy the various conln1unities in these Islands shouldtake concerted action against the tTIosquito. The reasons areself-evident. Not only does their presence detract frolll thenatural charll1 of the country, but the danger attending thepresence of a disease-carrying species is also apparent. N evv­comers are n10re susceptible to the attacks of this pest thanthe' kanlaainas and 1110ney could be profitably spent in n1ak­ing the stay of tourists n10re comfortable. The real e~tate deal­ers could well afford to atten1pt to rid any particular sectionof the mosquito nuisance for no one thing detracts more froma locality otherwise suitable for residential pUliposes thanthe presence of this pest.

1"'he one great rule of health and comfort in the tropics isto do away with or treat by methods well known to be ef­fective all standiJLg water because of the fact that only in suchplaces mosquitoes are known to breed.

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